Rubber treating process and product



Pat entecl May 19, 1.931

PATENT: OFFICE UNITED STATES CHARLES E. BRADLEY AND coiman rnnmrm, or mrsmwnxe, mnmna, as srenons TO msnawm RUBBER AND woornn MANUFACTURING comrm, or msnawaxa, INDIANA, a conronarron or INDIANA RUBBER TREATING PROCESS AND PRODUCT No Drawing, Application filed December Our invention relates to the preparation of rubber so as to improve its character for manufacturing purposes, and has reference more particularly to the method of treating the crude rubber, and the product resulting from such treatment, wherein the rubber is suitably softened to improve its milling, blending and calendering properties and to provide a finished. product of improved'quality. Crude rubber is broadly classified into two divisions, namely wild andplantation, and in each of these divisions there are various grades or qualities, some classified as hard and others as soft. 5 has been found heretofore for conditioning crude rubber to insure a fine homogeneous texture or uniform blending of these rubbers in compoundin and in the manufacture 0 rubber goods, t erefore, the gluality and texture of the finished product epends largely upon She class and grade of crude rubber emp oye In practice, the most satisfactory quality and texture is obtained by mixing varying uantities of soft rubber with the hard, wild ara rubber preferably being used in the compound, and particularly 'in certain classes of goods Where finer quality and smooth finished surfaces are desired, as the wild paraworks up into a more uniform and homog eneous texture than the plantation rubber. his is particularly important in products such as rubber footwear wherein the articles are fashioned from calendered sheets of rubber compound, as the smooth surface of the finished article depends, not upon moulding operations, but upon the character and condition of the rubber in the compound.

It is becoming more and more diflicult, however, to obtain supplies of satisfactory wild rubber, and there is therefore an urgent need especially in making high grade .calendered rubber goods, to adapt plantation rubber so that it may be satisfactorily used as a substitute for wild rubber, and in general to facilitate the blending and improve the quality and texture of rubber compounds.

This we have accomplished with our present invention by a treatment of the rubber 60 whereby it blends uniformly and affords a No satisfactory method 8.192s; Serial No. 74,198.

finished surface for rubber articles; to produce a soft grade of plantation rubber which may be used alone or in compound with hard f plantation rubber-to improve the quality and finished surface of rubber articles made therefrom; and in general to provide a simple and convenient method of treating crude rubber and a resulting product wherein improved milling, blending and calendering properties and uniform homogeneous texture of finished products are obtained.

In carrying) out our process, first grade plantation ru bers such as first latex crepe or smoked sheet is steeped for 24 hours in water at a temperature around 150 to 175 degrees Fahrenheit. By this step the rubber is swollen and whitened from the water taken up which amounts to 20 to 30 er cent by weight on the rubber. After this treatment the resulting swollen crude rubber is then sheeted, placed in a vulcanizer on racks and is then subjected to 25 to 50 pounds of live steam for one to two hours.

This subjectsthe rubber to a temperature between 267 degrees and 297 degrees Fahrenheit. It is then removed and dried in a vacuum drier at a temperature of from 15 to 25 pounds steam.

or it may be dried in an ordinary rubbe. dry kiln.

.We have discovered that rubber when swollen with water is particularly susceptible to heat and when a rubber thus swollen is heated under the above outlined conditions the nerve or kic of the crude rubber is materially reduced and a roduct is obtained which is more plastic an greatly improved I v in texture and calendering qualities. It is not sufiicient to steam the dry crude rubber as swelling with water preliminary to steamrapidly.

It is preferred to use steam as a heating agent and to avoid presence'of air in the heating process as high temperature air has an undesirable oxidizing'efi'ect on rubber.

'Moreover the desired wet condition of the rubber is also maintained during theheating with steam and the undesirable drying action of heated air on the rubber is avoided. It is suggested, therefore,'that if the rubber is heated otherwise than by the steam heating process described above, it would be desirable to place the wet rubber in a closed container, minimize the exposure of the rubber to air, and then heat the container so as to subject the rubber therein to the required tem erature.

T is rinciple of preparing first grade good ca endermg rubber would be adaptable to plantation practice and the heat could be applied there while the rubber was in the wet condition without utilizing the steeping operation.

The tensile,'wearand aging qualities of rubber compounds made from crudes softened by this process are approximately the same as those prepared from the same rubbers nottreated. In other words the good qualities of the crude are largely retained by this treatment which at the same time greatly improves the milling and calender- 111 properties of the rubber.

I liubber'compounds may be made with this softened rubber in the usual manner, by blending, for example, 20 to 30 per cent of the softened rubber with crude rubber of the hard quality, and this gives a compound having milling and calendering properties which have been obtainable heretofore only by using soft wild rubbers which itis now becoming very difiicult to procure. The rubber may be softened to a greater or less degree by varying the length of time it is heated as above su gested, so as to give the desired softness or the particular purpose for which the rubber is to be used, and the percenta e of soft rubber used in the... mixture may e varied accordin ly. In fact the rubber may be properly so nod so that 100 per cent of soft rubber is used instead of mixing a uantity of hard rubber therewith.

f it is dtsired to accelerate the softening of the rubber or to obtain a special soft grade the sofsoftener ber is first steeped in heated water, then subjected to-heating, preferably by direct application of steam under pressure and then dried, all in accordance with the process above described. The addition of the rosin or other softening agent accelerates the softoning action of the steam and makes it possible to obtain a thorough softening of the rubber to "the desired extent in a shorter period of heating or a softer grade of rubber may be obtained. I

While we have described the preferred ,manner of carrying out our invention we are aware that various changes and modifications may be made without departing from the principles of our invention the scope of which is to be determined by the appended claims.

Weclaim:

1. The method of softening rubber which com rises heating water soaked crude rubber or approximately an hour or more at atemperature above the boiling point of water 7 while maintaining the rubber in the watersoaked condition.

2. The method of softenin rubber, which comprises subjecting crude ru bercontaining at least ten percent of moisture to heat above the boiling point of water and pressure above atmospheric while substantially preserving such moisture therein, and then drying the rubber.

3. llhe method of softening rubber which comprises heating a water soaked compound of crude rubber-and a softening agent.

4. The method of improving the milling and calendering properties of rubber which comprises preparing crude rubber with a ,moisture content in excess of ten percent,

then subjecting the rubber in a closed container for approximately an hour or more to substantially 25 to 50 pounds of live steam, and

then drying the rubber.

5. The meth d of improviiig the milling and calendering properties of rubberwhich comprises steeping crude rubber for substantially 24 hours in water at a temperature subjecting the resulting rubber in a closed container to substantially 25 to 50 pounds of live steam, and then drying the rubber.

around to 200 degrees Fahrenheit, then H and calendering properties of plantation rub- I in heated water, then softening the rubber by heating the rubber under conditions which preserve the moisture in the rubber dulrling the heating, and then drying the ru er.

8. The method of producing calendered sheets ofrubber which comprises swelling crude rubber in hot water, then heating the resulting swollen rubber with live steam, then drying the rubber and then calendering the dried rubber.

9. The method of producingealendered sheets of rubber which comprises steeping first grade plantation rubber for approximately 24 hours in water at a temperature around 150 to 175 degrees Fahrenheit, then sheeting and racking the resulting rubber and exposing same for approximately one to two hours to live steam at 25 to 50 pounds pres sure, then drying the sheeted rubber and then subjecting the rubber to calendering rolls.

10. A rubber product obtained by subjecting crude rubber while it retains a substantial amount of moisture in excess of hydro scopic and condensation moisture to heat substantially in excess of the boiling point of water and pressure substantially in excess of atmospheric without substantial drying and thereafter drying the rubber.

11. A rubber product for making calendered sheets comprising crude rubber swollen iin hat water and then successively heated and ne Y 12. A rubber product for making calendered sheets comprising plantation crude rubber in the form resulting from first stee ing the crude rubber in hot water, then-s0 ening underheat and then drying.

13. A rubber product comprising plantation crude rubber having the properties, obtained by first uniformly saturating the crude plantation rubber with water, then subjecting the saturated rubber for approximately one to two hours to live steam at 25 to 50 pounds of pressure, and then drying the rubber.

14. Plantation rubber having improved calendering and milling properties obtained by subjectmg the crude rubber with a moisture content 1n excess of ten per cent to steam and pressure for substantially an hour or more.

15. The method of softening rubber which comprises subjecting rubber uniforml impregnated with moisture substantially in excess of hydroscopic and condensation mois-' moisture substantially form moisture impregnation of the rubber.

16. The method of. softening rubber which comprises subjecting rubber uniforml impregnated with moisture substantially 1n excess of hydroscopic and condensation moisture for a substantial length of time to a heated atmosphere substantially devoid of air and at the same time preserving said moisture in the rubber.

17 The method of softening rubber which comprises subjecting rubber uniforml impregnated with moisture substantially in excess of hydroscopic and condensation moisture for a substantial length of time to steam and pressure and at the same time preserving said moisture in the rubber.

18. The method of softening-rubber which comprises subjecting" rubber'uniforml impregnated with moisture substantially in excess of hydroscopic and condensation moisture for a substantial length oftime to a heated atmosphere at a pressure substantially above atmospheric while preserving said uniform moisture impregnation of the rubber.

product obtained by sub- 19. A rubber jecting rubber umformly impregnated with moisture substantially 1n excess of hydroscopic and condensation moisture for a sub stantial length of time to a heated atmosphere while preserving said uniform moisture impregnation of the rubber.

20. A rubber product obtained by subjecting rubber uniformly impregnated with in excess of hydroscopic and condensatlon moisture for a substantial length of time to a heated atmos phere substantially devoid of air and at the same time preserving said moisture in the rubber.

21. A rubber product obtained by subjecting rubber umformly impregnated with moisture substantially in excess of hydroscopic and condensation moisture for a substantial length of time to steam and pressure and at the same time preserving said moisture in the rubber.

22. A rubber product obtained by subjecting rubber uniformly impregnated with moisture substantially in excess of hydroscopic and condensation moisture for a sub stantial length of time to a heated atmosphere at a pressure substantially above atmospheric while preservin said uniform moisture impregnation oft erubber. o

CHARLES E. BRADLEY. CONRAD FERRETTIE. 

